Monday, 30 December 2013

Defending Liverpool's Defence

With the season about to start, I thought I would follow up to piece that I did earlier in the year looking at how Liverpool’s form changed over the season, however whilst that looked at attacking form, this one looks at Liverpool’s defensive form. Again I will look at Liverpool’s performance compared to how the league performed on average, how the top 4 performed, and also compared to Liverpool in the 2011-12 season, as well as having the short term form by having the 6-game moving average. One thing to note is that due to there being fewer observations, for example Liverpool conceded far fewer shots, goals etc., that the graphs show more extreme changes compared to the attacking versions of these graphs

I’ll start by looking at shots conceded per game. Apart from the 18 shots conceded in the first game of the season against West Brom skewing the averages, Liverpool performed more or less in line with the Top 4 teams throughout the season.

In terms of the accuracy of opposing team’s shots, despite the slow start that Liverpool had and perhaps surprisingly, they actually allowed significantly less shots to hit the target compared to the Top 4 teams and the rest of the league over the first half of the season, whilst over the 2nd half of the season, a greater percentage of opponents shots were hitting the target.

Moving on to Opponent Shots Conversion and Shots on Target Conversion, we can see how poorly Liverpool defended and Pepe Reina performed in the opening 5 or 6 games of last season. Basically, Liverpool defended and kept goal more or less like a lower league team when going up against a Premier League side in a cup, but this quickly regressed to the mean, and they performed like a Top 4 team from game 7 onwards (in the moving-average plot, this shows up from match 12). Those first 6 games had such an impact though that the end of season conversion rates were still only in line with the league as a whole.

How do Liverpool, or more pertinently Pepe Reina and Brad Jones, do at keeping out Clear Cut Chances (CCC)? So what is a CCC? It is one of Opta’s few subjective stats that can broadly be described as a chance where the attacker is probably central to goal with only the keeper to beat. So a keeper would hope to either save it, or perhaps attempt to put the attacker off sufficiently that they miss. As I mentioned in the original piece, the conversion rate for CCCs is much more variable than the other conversion rates, this is because in some games there will be few or even no CCCs, which means that both very high and very low single game conversion rates are far more likely, and we see this clearly in Liverpool’s form plot (note that the reason you can’t see the league average plot is because it was the same as the Top 4). Again, Liverpool started poorly, but were better than the Top 4 teams from match 7 onwards, apart from a large peak at match 17 where all the CCCs that Liverpool faced were scored giving a 100% conversion rate. More specifically, it was in fact a 4 match period with the goals coming from Tottenham, West Ham and Aston Villa.

With that in mind, it is interesting to then see the rate at which Liverpool were giving up CCCs per game through the season. Again we see Liverpool started off poorly, giving away on average 1.5 CCCs over the first 10 games, but by match 17, where we saw the 100% conversion rate, the 6-game form had fallen to 0.7 per game. So, it was only 4 out of 4 CCCs conceded in 6 games. As the average conversion rate for all CCCs is around 38%, it is a bit like tossing a coin 4 times and getting 4 heads, so I don’t think we should put it down to poor goal keeping. You’ll notice there is a sharp rise in CCCs conceded from about match 20, but this coincided with an increase with CCCs for Liverpool, and can perhaps be put down to increased attacking leaving the defence more open (Note: Liverpool’s average in 2011-12 was the same as the Top 4’s last season).

Finally I’m going to look at Errors per Game. It should be noted that these are ‘on the ball’ errors, so does not include an error like not marking the run of an opponent from crosses (something that had many Liverpool fans pulling their hair out). Again we see the effect that Liverpool’s poor start to the season had, however it took longer for Liverpool to recover from than compared to the other metrics, but by the end of the season, on the ball errors had almost become non-existent. Over the season as a whole, only Arsenal and Newcastle made more errors than Liverpool’s 36, however if you split the season in half, over the first 19 games Liverpool made 28 errors, over the last 19 games it was only 8. As an on the ball error will often leave the rest of the defence wrong footed, these types of errors tend to have a high conversion rate, and Liverpool conceded 10 goals from the 36 errors they made. If Liverpool can continue to keep the error rate at the level of the 2nd half of the season, then there would be a lot less hair pulled out by the fans this coming season.

Perhaps it was the tough start Liverpool had, perhaps it was the getting used to Brendan Rodgers system, or perhaps they were just unlucky (probably a combination of all 3), but clearly Liverpool started the season really badly last year. If they can perform defensively as well as they did over the last 30 or so games, they could well turn a few of those losses and score draws into wins, and have a good crack at finishing in the top 4.

About Me

Another blog mainly about football stats, and another blog mainly about Liverpool. But have you seen one with football finance and fantasy football as well? Yes, you probably have.
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